The weber carb needs 2-4psi. Any more then when you turn the engine off gas will wash oil off the cylinder walls and it'll kill your engine over time.

The stock mechanical pump puts out 7psi, the stock efi pump puts out 50 something psi. I once tried to use a regulator on the stock electrical pump and it couldn't hold all the pressure and would blow the lines off. The regulator works fine with the mechanical pump. You can also buy an adjustable aftermarket electric pump and then you wont need a regulator.

What ever you do, make sure you get the psi down below 4psi and you'll be fine.

-Scerb